ANSI B17.2 Woodruff Key & Keyseat Dimensions Calculator (+ DIN 6888)
Under ANSI/ASME B17.2, a Woodruff key number encodes its exact geometry: the last two digits give the nominal cutter diameter in eighths of an inch (D_c = [Key# % 100] / 8"), and the preceding digits give the key width in thirty-seconds of an inch (W = [Key# // 100] / 32").
Interactive ANSI B17.2 Woodruff Key Decoder & Milling Plunge Calculator
Decode standard Woodruff key numbers (#204 to #1212), calculate cylindrical shaft arc crown height (h_c), total radial cutter plunge (B + h_c), and micrometer over-shaft check (S).
How Do You Decode ANSI B17.2 Woodruff Key Numbers (#204 to #1212)?
Semicircular Woodruff keys are widely specified on tapered machine tool spindles, automotive crankshafts, marine propellers, and small electric motor shafts because the deep circular pocket prevents the key from tipping or rolling out under cyclic torsional vibration, and the curved bottom self-aligns with tapered hub keyways. Under ASME Geometric & Mechanical Standards (ANSI/ASME B17.2) and Machinery's Handbook (Industrial Press) fastener standards, every American Woodruff key is identified by a 3-digit or 4-digit code number that directly defines the milling cutter required to machine the slot.
To decode any ANSI B17.2 Woodruff number, split off the final two digits and divide by 8 to obtain the semicircular key diameter (which matches the nominal Woodruff keyseat milling cutter diameter D_c in inches); then take the leading digit(s) and divide by 32 to obtain the key thickness width W in inches. For example, a #608 Woodruff key has a leading digit of 6 (W = 6/32" = 3/16" = 0.1875" wide) and trailing digits of 08 (D_c = 8/8" = 1.000" diameter). Similarly, a #1008 key is 10/32" = 5/16" wide by 8/8" = 1.000" diameter, while a #1212 key is 12/32" = 3/8" wide by 12/8" = 1.500" diameter.
| ANSI Key No. | Key Width (W) | Cutter Dia (D_c) | Key Height (H) | Shaft Depth (B) | Projection (C) | Hub Depth (E) | Rec. Shaft Dia |
|---|---|---|---|---|---|---|---|
| #204 | 1/16" (0.0625") | 1/2" (0.500") | 0.203" | 0.1668" | 0.0312" | 0.0372" | 0.375" – 0.500" |
| #304 | 3/32" (0.0938") | 1/2" (0.500") | 0.203" | 0.1511" | 0.0469" | 0.0529" | 0.500" – 0.625" |
| #305 | 3/32" (0.0938") | 5/8" (0.625") | 0.250" | 0.1981" | 0.0469" | 0.0529" | 0.500" – 0.750" |
| #404 | 1/8" (0.1250") | 1/2" (0.500") | 0.203" | 0.1355" | 0.0625" | 0.0685" | 0.625" – 0.875" |
| #405 | 1/8" (0.1250") | 5/8" (0.625") | 0.250" | 0.1825" | 0.0625" | 0.0685" | 0.688" – 0.938" |
| #406 | 1/8" (0.1250") | 3/4" (0.750") | 0.313" | 0.2455" | 0.0625" | 0.0685" | 0.750" – 1.000" |
| #606 | 3/16" (0.1875") | 3/4" (0.750") | 0.313" | 0.2143" | 0.0938" | 0.0998" | 1.000" – 1.250" |
| #608 | 3/16" (0.1875") | 1" (1.000") | 0.438" | 0.3393" | 0.0938" | 0.0998" | 1.125" – 1.375" |
| #808 | 1/4" (0.2500") | 1" (1.000") | 0.438" | 0.3080" | 0.1250" | 0.1310" | 1.375" – 1.750" |
| #1008 | 5/16" (0.3125") | 1" (1.000") | 0.438" | 0.2768" | 0.1562" | 0.1622" | 1.625" – 2.000" |
| #1212 | 3/8" (0.3750") | 1-1/2" (1.500") | 0.641" | 0.4485" | 0.1875" | 0.1935" | 2.000" – 2.500" |
How Do Machinists Calculate Total Radial Milling Cutter Plunge Depth (B + h_crown)?
When milling a Woodruff keyseat into a cylindrical shaft of diameter D_shaft on a horizontal or vertical knee mill, blueprints specify the vertical keyseat depth B measured from the sheared chordal side wall of the slot down to the bottom of the semicircular arc. However, when you touch the outer periphery of your Woodruff cutter against the top tangent crest of the round shaft to set your Y-axis or X-axis DRO zero, the cutter touches the curved crown of the shaft—which sits higher than the flat chordal side wall by the Cylindrical Arc Crown Sagitta (h_c)!
From exact circular trigonometry traceable to NIST (National Institute of Standards and Technology) and ISO International Metrology Standard geometry, the shaft arc crown height across a slot of width W is h_c = (D_shaft - √[D_shaft² - W²]) / 2. Therefore, after touching off the outer periphery of the Woodruff cutter on the outside crest of the shaft, you must feed the cutter radially inward to a Total Milling Plunge Depth of Plunge = B + h_c. To verify the finished pocket depth before unclamping the shaft, measure from the bottom of the slot to the opposite outside surface of the shaft using a point-anvil micrometer or depth gauge; the reading must equal S = D_shaft - B - h_c within +0.000" / -0.005".
| DIN 6888 Designation | Width (b) | Cutter Dia (d2) | Key Height (h) | Shaft Depth (t1) | Hub Depth (t2) | Shaft Range (d1) |
|---|---|---|---|---|---|---|
| 3 × 3.7 | 3.0 mm | 10.0 mm | 3.7 mm | 2.5 mm (+0.1/0) | 1.4 mm (+0.1/0) | 10 – 12 mm |
| 4 × 5.0 | 4.0 mm | 13.0 mm | 5.0 mm | 3.5 mm (+0.1/0) | 1.7 mm (+0.1/0) | 12 – 17 mm |
| 5 × 6.5 | 5.0 mm | 16.0 mm | 6.5 mm | 4.5 mm (+0.1/0) | 2.2 mm (+0.1/0) | 17 – 22 mm |
| 6 × 7.5 | 6.0 mm | 19.0 mm | 7.5 mm | 5.1 mm (+0.1/0) | 2.6 mm (+0.1/0) | 22 – 30 mm |
| 8 × 9.0 | 8.0 mm | 22.0 mm | 9.0 mm | 6.0 mm (+0.2/0) | 3.2 mm (+0.2/0) | 30 – 38 mm |
| 10 × 11.0 | 10.0 mm | 28.0 mm | 11.0 mm | 7.5 mm (+0.2/0) | 3.7 mm (+0.2/0) | 38 – 44 mm |
How Do Metric DIN 6888 Woodruff Keys Compare to Rectangular Parallel Keys?
In European and ISO metric machinery, semicircular keys are governed by DIN 6888 and designated by Width b × Height h in millimeters (for example, DIN 6888 6 × 7.5 uses a 19.0 mm diameter cutter to cut a 6.0 mm wide slot to a shaft depth t_1 = 5.1 mm). Like rectangular parallel keys under DIN 6885, DIN 6888 specifies three fit classes for the keyseat width b: a tight interference shaft fit (P9) paired with a close hub fit (JS9) for reversing torque loads, or a normal runner fit (N9 shaft / JS9 hub) for unidirectional drives.
Because a semicircular Woodruff keyseat cuts significantly deeper into the shaft core (t_1 ≈ 2.0× deeper than a flat rectangular keyseat), it increases torsional and bending stress concentration factors (K_t). Never place two Woodruff keys 180° opposite each other on a high-load shaft; for heavy torque transmission on shafts larger than 2.0" (50 mm), switch to a standard parallel key using our ANSI B17.1 & DIN 6885 Rectangular Keyway Calculator. You can also check shaft interference fits on our Shaft & Hub Press-Fit Calculator, ISO 286 Hole & Shaft Tolerance Calculator, and Retaining Ring Groove Dimensions Chart.